1. Field of the Invention
The present invention is generally in the field of semiconductor devices and their fabrication. More specifically, the present invention is in the field of high electron mobility transistors and their fabrication.
2. Background Art
Many prevalent electronic devices and systems continue to require faster switching speeds and greater power handling capabilities. Examples of such electronic devices and systems are semiconductor based switching and amplification devices employed in, for example, wireless communications such as W-CDMA (wideband code division multiple access) base stations and the like.
One solution to the increased device performance demands has been the development and implementation of high electron mobility transistors (HEMTs), such as the heterostructure field effect transistor, or HFET. In a typical HFET, a two-dimensional electron gas (2DEG) is generated at a semiconductor heterojunction. The 2DEG represents a very thin conduction layer of highly mobile and highly concentrated charge carriers free to move readily in the two dimensions of that conduction layer, but constrained from movement in a third dimension perpendicular to the conduction layer.
In practice, the ability of an HFET to perform well at high frequency and/or at high power, depends in part on the characteristics of the 2DEG generated at the semiconductor heterojunction. In particular, where charge carriers are insufficiently constrained from moving away from, or dispersing out of, the thin conduction layer, for example by movement perpendicular to the conduction layer towards the device substrate, device performance is adversely affected. Unfortunately, conventional approaches to HFET fabrication have either failed to provide optimal charge carrier constraint within the 2DEG, or in seeking to improve confinement of the charge carriers, have produced other undesirable results negatively impacting device performance.
Thus, there is a need to overcome the drawbacks and deficiencies in the art by providing a HEMT, such as an HFET, exhibiting more effective containment of charge carriers by preventing charge carrier migration out of the semiconductor active region.